2 replies to this topic

[SPBK]

Hi,

 

 

As a scope of project , we are adding new two pipeline pumps in parallel to the existing  two pipeline pumps(30 Year old)  with similar capacity.

 

Major difference is that new  selected pumps are provided with Variable Frequency Drive (VFD) to meet different flow scenarios economically.

 

 

Existing piping system is designed for 68 barg.

 

Selected new pumps have shut off head of  76.76  barg  at 105% rated pump speed.Hence to safeguard existing pipeline from new shut off we are providing,

 

1. Pressure High High Trip at 67 barg at new pipeline pumps common discharge to stop new pumps.

2. Pressure safety valve at new pipeline pump common discharge line which is set at 68 barg.

 

I have sized  pressure relief valve considering pump blocked in condition as governing case with pump rated flow at rated rpm(liquid relief rate).

 

But client process engineer comp  up with comment that relief rate shall be taken from  selected pump curve at 105% rated speed  corresponding to set pressure of PSV(68 barg). Which call for higher relief rate.

 

It will be great help for me, which is right relief rate for PSV sizing with relevant reference guidelines.

 

 

I am herewith attaching selected pump curve.

 

 

 

 

Attached Files

•  S25C-213042913530.pdf   407.8KB   15 downloads

[fallah]

SPBK,

 

It depends on pump control logic/system, its reliability and safety level. If the scenario of pump working at 105% rated pump speed while discharge line is blocked would be credible, then your client is right and the relief rate shall be taken from selected pump curve at 105% rated speed corresponding to set pressure of PSV(68 barg).

[SPBK]

Thanks Fallah,

 

addition two safety layer, we are also providing Third safety by tripping VFD art 105% of rated speed.

 

Per a pump affinity law shall we can consider flow corresponding to 105% of rated speed.

 

does we have any guidelines/STD in this regards.

 

Thank you very much once again.

 

 

if any have gone through similar case.